Appraisal of the current staging system for residual medulloblastoma by volumetric analysis

Aim: This study aims to investigate the accuracy of the current staging system of childhood medulloblastoma by using volumetric image analysis on immediate post-operative MRI scans. Material and methods: Tumour volume and maximum cross area of residual medulloblastoma were measured on immediate post-operative MR scans of 37 children operated between 1999 and 2005. Results: Mean preoperative volume was 32 cm³ (range 4.5-71.9 cm³). Mean post-operative volume was 3.3 cm³ (range 0-23.3 cm³). At mean follow-up of 50.08 months (range 6-129), 15 (40%) patients had died. Cut-off limit for residual post-operative tumour volume employed was maximum cross section of 1.5 cm², which corresponds to volume of 1.376 cm³; 14 patients (38%) had no residual tumour, 7 patients (19%) had less than 1.5 cm² and 16 patients (43%) had more than 1.5 cm ² residual tumour in its maximum cross section area. In three patients (8.2%) there was mismatch between the measured maximum cross section area and volume. In particular, in two patients, the cross section areas were more than 1.5 cm² but the residual tumour volumes were less than 1.376 cm³ (the cross section area overestimated the residual volume) and in one case, the cross section area was less than 1.5 cm² but the residual tumour volume was more than 1.376 cm³ (the cross section area underestimated the residual volume; difference statistically significant, Fisher's exact test, p<0.01). Conclusions: It appears that volumetric measurement of residual medulloblastoma on immediate post-operative MRI scans may further improve the accuracy of staging process.